This current generally relates to low gas flow plasma electron current arc sources for use in a vacuum environment. The arc head disclosed is of a hollow cathode type where a propellant, reduced to a gaseous state, is ionized by electron bombardment from a low work function emitter of copious quantities of thermal electrons. The electron current drawn from this type of arc head can be used for a variety of space and ground based purposes which include vacuum arc welding, vacuum metal vapor deposition, ion beam and spacecraft charge neutralization, and as a propulsion device for spacecraft attitude and orbit maintenance and repositioning functions.
Hollow cathode arc sources for use in a vacuum environment are known. Typically, the hollow cathode is in the form of a tube with one end either open or stopped down, with electrons originating from the tube walls or from a low work function material impregnated structure within the tube, and with the hollow cathode tube structure initially heated to electron emitting temperatures either by indirect resistance heating or by direct heating from glow discharge processes. The arc from simple open tube hollow cathodes has been used for vacuum welding as has the arc from a simple stopped down hollow cathode. Attention is directed to U.S. Pat. No. 5,149,932 by R. M. Poorman and J. L. Weeks. Disadvantages of this type of hollow cathode for vacuum welding are that voltages as high as 20,000 volts are required to initiate the arc, the electron emission occurs at very high temperatures promoting component erosion and short life time, coolant is required, gas flow rate requirements are relatively high, arc start-up is not completely reliable or well defined, and melt zone penetration is poor.
Prior art hollow cathode arc sources for vacuum arc welding have been limited in their usefulness and ease of operation.